From time to time, an internal combustion engine of a hybrid vehicle may be stopped while the hybrid vehicle continues to move along a drive path. The internal combustion engine may be stopped to conserve fuel while an electric machine provides propulsive effort or converts kinetic energy of the hybrid vehicle into electrical energy. Electrical energy produced by the electric machine may be stored for later use in a battery, capacitor, or other electric energy storage device. While the electric machine may be rather efficient at converting the vehicle's kinetic energy into electrical energy, a substantial amount of the vehicle's kinetic energy may still be lost. Therefore, it may be desirable to improve the efficiency of converting the vehicle's kinetic energy into electrical energy.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: stopping rotation of an engine of a vehicle in response to an engine stop request while the vehicle is moving; and ceasing to rotate a first input shaft and a second input shaft of a transmission at a gear ratio multiple of a transmission output shaft speed in response to the engine stop request while the vehicle is moving, the transmission directly coupled to the engine.
By ceasing to rotate first and second transmission input shafts at a gear ratio multiple of a transmission output shaft speed, it may be possible to reduce losses associated with rotating transmission input shafts and convert a portion of a vehicle's kinetic energy that would otherwise be used to rotate transmission shafts into electrical energy. In particular, rotation of transmission input shafts may be stopped in response to stopping engine rotation or a request to stop engine rotation so that a vehicle's kinetic energy is not used to rotate transmission input shafts. The vehicle's kinetic energy may then be converted into electrical energy via an electric machine in the driveline so that a larger portion of the vehicle's kinetic energy may be converted into electrical energy. Further, in examples where improved vehicle response has higher priority than improving driveline efficiency, transmission gears may be shifted and pre-selected while the vehicle is moving and while the engine is stopped to reduce an amount of time to couple an engine to vehicle wheels.
The present description may provide several advantages. Specifically, the approach may improve efficiency of converting a vehicle's kinetic energy conversion into electrical energy. Further, the approach may reduce an amount of time to restart an engine and provide engine torque to vehicle wheels. Further still, the approach may reduce driveline torque disturbances if engine restarting is requested.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.